Fuel used in an internal combustion engine, in particular fossil fuel, contains trace amounts of sulfur (S) ingredients. The sulfur ingredients contained in fuel in this way invite deterioration of component parts in an exhaust system of an internal combustion engine etc. Further, if frequently performing control suppressing deterioration of the component parts due to the sulfur ingredients or control for regenerating deteriorated component parts, deterioration of the fuel efficiency is invited. Therefore, to keep the deterioration of the fuel efficiency etc. at a minimum extent while keeping the deterioration of the component parts at a minimum extent, it is desirable to detect the content of sulfur ingredients in the fuel.
If the fuel used in an internal combustion engine contains sulfur ingredients, the exhaust gas discharged from a combustion chamber contains sulfur oxides (SOX). Further, the higher the content of the sulfur ingredients in the fuel, the higher the concentration of SOX in the exhaust gas. Therefore, if possible to detect the concentration of SOX in exhaust gas, it is possible to estimate the content of sulfur ingredients in the fuel.
Therefore, an exhaust gas sensor detecting the concentration of the SOX or other oxygen-containing gas components in the exhaust gas has been proposed (for example, see Japanese Patent Publication No. 11-190721A). This exhaust gas sensor has a measured gas chamber in which exhaust gas is introduced through a diffusion regulating layer, a first electrochemical cell, and a second electrochemical cell. In the first electrochemical cell, a relatively low voltage is applied across the electrodes forming the first electrochemical cell. As a result, due to the oxygen pumping action of the first electrochemical cell, the oxygen in the measured gas chamber is removed without the SOX in the measured gas chamber being decomposed. On the other hand, in the second electrochemical cell, a relatively high voltage is applied across the electrodes forming the second electrochemical cell. As a result, the SOX contained in the exhaust gas after removal of oxygen by the first electrochemical cell is decomposed. In addition, the oxide ions generated due to the decomposition of this SOX are discharged from the measured gas chamber due to the oxygen pumping action of the second electrochemical cell and the concentration of SOX in the exhaust gas is detected by detecting the decomposition current flowing along with the discharge of oxide ions.